I. Field of the Invention
The present invention relates generally to the field of plant molecular and cellular biology. More particularly, it concerns methods and compositions comprising altering fertility in plants through modulation of flower GABA levels.
II. Description of Related Art
The goal of plant breeding is to combine various desirable traits in a single variety/hybrid. Breeding techniques take advantage of a plant's method of pollination. There are two general methods of pollination: a plant self-pollinates if pollen from one flower is transferred to the same or another flower of the same plant. A plant cross-pollinates if pollen comes to it from a flower on a different plant. Control of the mode of fertilization is crucial to a successful plant breeding scheme.
One use of plant breeding techniques is the development of hybrid varieties. This is because a number of important crop plants exhibit hybrid vigor, whereby hybrid plants are grown by farmers because they exhibit enhanced agronomic characteristics, including more vigorous growth. As the hybrid crops are preferred, development of hybrid varieties of seed is important to the seed industry.
For production of hybrid crops, it is generally necessary to take steps to prevent self-pollination. In the case of hybrid maize production, this is typically achieved by physically removing the male reproductive flower portions, or tassels, prior to pollen shed. Although effective, the technique is highly labor intensive. Further, in plant species with individual flowers with both male and female reproductive organs, this can be difficult or impossible and another system for regulating fertility is generally needed.
Another means for controlling self pollination is the use of genetic male or self-sterility. A number of genes conferring male sterility have been described, for example, in U.S. Pat. No. 3,861,709, U.S. Pat. No. 3,710,511, U.S. Pat. No. 4,654,465, and U.S. Pat. No. 5,625,132. However, these genetic factors, whether nuclear or cytoplasmic, can be difficult to stably maintain in parent lines. Where cytoplasmic male sterility (CMS) is used, hybrid seed production requires three inbred lines: (1) a cytoplasmically male-sterile line having a CMS cytoplasm; (2) a fertile inbred with normal cytoplasm, which is isogenic with the CMS line for nuclear genes (“maintainer line”); and (3) a distinct, fertile inbred with normal cytoplasm, carrying a fertility restoring gene (“restorer” line). The CMS line is propagated by pollination with the maintainer line, with all of the progeny being male sterile, as the CMS cytoplasm is derived from the female parent. Therefore, although possible, maintenance of the male sterile line can be difficult and labor intensive. Further, the male sterility trait may introduce undesirable characteristics in the plant. For example, some cytoplasmic male sterility factors have been associated with increased susceptibility to fungal pathogens.
Various chemical gametocides have also been described for control of pollination. Gametocides affect processes or cells involved in the development, maturation or release of pollen. Plants treated with such gametocides are rendered male sterile, but typically remain female fertile. The use of chemical gametocides is described, for example, in U.S. Pat. No. 4,936,904. While use of gametocides has proved beneficial in some cases, they have yet to be adopted for widespread use.
Although the prior art has provided useful systems for the regulation of plant fertility, there is still a great need in the art for improved systems for regulating plant fertility. In particular, there is a need for a system of inducing self-sterility that avoids the requirement for costly emasculation of plants or complicated breeding schemes. The development of such a new system would improve plant breeding techniques and represent an important advance in the field of agriculture.